What are you guys that have done/are doing the 4.6 with the 4R70W tranny swap using for rear end ratios? I'm going to have to address that sometime this year, and I think what I remember being recommended is a 3:50 (3:55?) gear ratio because of the OD. I don't want it to be a dog "off the line", but my primary concern is reasonably low rpm's at a 70ish cruising speed.
I do want to keep the oem '57 case, but I'll have it narrowed and set up for discs.
My 10 F150 is 3:55 and runs 2250 at 80 MPH. The Mustang is 3:73 and runs 2500 at 80. The 93 F150 with a 3:55 ran right at 2300 at 80. The 66 Falcon Ranchero with a Mustang 5 speed and a 3:23 ran...no idea...at 80 but made gas running 65 - 70, it sounded like it was in the mid to high teens.
Rich:
Don't forget the trucks tires are much taller than what you will be using so the engine RPM would be lower. My transmission guy tells me your 4R70W's overdrive ratio is 0.70. That's a good starting point for this discussion. My Shelby GT with it's 3:55 rear gears gets as high as 24 mpg when cruising long distances at 75 - 80 mph. The final drive ratio in my overdrive is 0.71 and my RPM's @ 80 mph are about 2300. My tires are probably a bit smaller diameter than what you will be running. My guess is that either a 3:50 or 3:70 gear would give good all around drivability. What the heck, if you don't pick the right gear to start with, your Ford 9" has the ability to take pretty much any gear you could want. Enjoy your final assembly and road testing, you have one heck of a great ride.
Bob
57 AGIN
The 4R70W has a 2.40 first gear, that seems very tall. If f you go with a 3.89 rear end ratio that gives you the equivalent of a 2.72 overall ratio on the road. running 26" diameter tires you should see 2110 rpm at 60mph, 2813 rpm at 80 mph. That seems reasonable. A 4.10 would be better for acceleration. this would give you 2224/60 and 2964/80. Personal preference. These rpm/speed/tire diameter numbers are directly proportional, in other words a 27" tire would reduce rpm by 26/27. A 3.55 ratio would reduce the rpm by 3.55/3.89.
Good info, Bill
Thanks Bob...I think you just unknowingly(or knowingly) cleared up some confusion I had..3:50's or 3:55's. From your post I'm assuming what your saying is the one available for the '57 9" are 3:50's, and it's the newer differentials (8.8's?), like your Shelby, and Bill's trucks, that have the 3:55's. Is that correct?
No, mine's a budget build, and I'm guessing around 1K-1200 just for the tracloc gear set, so If I don't get it right, I'm gonna be stuck with it no matter how many other options might be available.
Lynn, I'll have to digest all that info.
Wasn't trying to confuse the issue....
Rear end ratios depend on the number of teeth on the pinion. A 9 tooth pinion can have ratios of 35/9 or 3.89, 34/9, 32/9 or 3.55. The numbers have to be whole since you can't have a fraction of a tooth on a gear. A 10 tooth pinion will give even different numbers... 35/10 or 3.50. Math fun with cars!!! :003:
Well I may finally be seeing the light on the differential mystery...So, the 35,34,32 numbers come from the number of teeth on the ring gear, (if that terminology is correct).. Do the '57 era differentials have both the 9 tooth or 10 tooth pinions available?
I am pretty sure just looking at the ratios that '57s all had 9 teeth pinions. Just a guess, but I think the pinion number of teeth stays constant for a given differential design.
the gear ratios for the 4r70w are 2.84 first,1.55 second,1to1 3rd,0.7 od.i am using a 3.56 axle ratio[ford used 3.56 till 1969 then went to 3.50].this gives me a 10to1 overall first gear ratio.and with my tire size will be turning about 2100 at 70 mph in od
I saw 2.4 on the web for late 80s early 90s Lincolns. Thought that was very tall.... 2.84 makes more sense. I think you must look at the overall gear ratios to pick a rear end ratio.
The 57 Ranchero has a 3:56 (tag is on the housing), the 57 Ranchwagon had a 3:89 and the Edsel has a 2:91. All are 9".
The 8.8s are 3:55 in the truck, the GT500 had 3:55s and I put 3:73s.
The Explorer rears (95 - 01) came with 3:55, 3:73 or 4:11.
No idea how the pinion tooth to ring gear thing works, I just count both and do the math.....:<)
Rich if it were me I would use the stock 3:56 as my 98 MK VIII LSC was a 3:55 and gave great milage as well as performance.
9 teeth and 9 inch no relationship, I agree.... do the math. If one has a 3.50 or a 4.10 ratio they don't have a 9 tooth pinion....
I'm pretty sure my oem is 3.56....I took the tag off years ago to clean it up so I could read it, and lost it. If I was keeping the single drive axle, I'd probably just keep the stock gears, assuming they checked out ok, but I am wanting to change to the trac-loc.
As long as I'm getting an education here...where/what does the term "tall" come in, or, what does it mean?
if your car was a 6 cyl. std trans,they usually came with 3.70 axle ratio.tall,long legged,high speeded is used to talk about a ratio closer to 1to1
Rich:
If I'm correct, and of course I think I am (lol) I believe the following to be the way it is. If you have a "tall" gear in the rear end it is a gear that is meant for very good gas mileage. While a "low" gear ratio is one that is suited for quicker acceleration. When I was young this just didn't make sense, as we all know that a 4:11 gear was the one used back then if you wanted acceleration (now days a number of quarter mile racers use a 5:38 ratio and buzz their motors to 10,000 rpm). The thing that didn't make sense was a "low" gear had a larger number than a "tall" gear. That's bass ackwards, isn't it. But, that is the way it is, at least I think it is????
When I had my 65 Mustang I had two gear sets, a 3:50 and a 4:57. I can tell you quite positively that driving my 65 between LA and San Diego to and from home to my ship board duty station that if I had gone racing that weekend with the 4:57's installed, I was turning about 4,000 rpm at normal freeway speeds. The rpm's dropped considerably when I ran the 3:50's, but so did that wonderful feeling of getting pushed back in the seat when the foot hit the gas pedal to get onto the freeway. Man those were really good old days. The same hold true today, before I put in the TKO 600 with it's 0.64 overdrive gear, when I wanted to change lanes on the freeway I didn't have to down shift into 3rd. All I had to do was hit the gas pedal and I'd accelerate like a bat out of xxxx and be in the next lane. Now I have to think about making a leisurely lane change in 5th gear or dropping down a gear and stepping on the pedal.
With the overdrive in the 4RW70 you plan on installing having a slightly lower rear end gear shouldn't cause you problems. It will help getting you car moving and once you get into the OD gear the rpm will come down to not much over 2,000 to 2,300 rpm.
Bob
57 AGIN
A "tall" (lower numerically) rear end gives you higher top speed but less acceleration. A "low" (higher numerically) rear end gives you lower top speed but greater acceleration. Confusing, I learned to remember based on top speed.... tall/high, low/slow.
The mystery is unraveling very quickly guys, thanks. Some more "do I have this right?"'s.....
I'm assuming that the "closer to a 1:1 ratio" that Gary mentioned, and Bob and Lynn were refering to: That is the ratio of the differential's gear to the tranny's 1st gear?
Also...the ring gear as stated can have a different number of teeth, while the pinion gear remains constant at, in our case, 9 teeth. I'm trying to figure out how a ring gear can have a differing quantity of teeth, so I'm concluding that the difference has to come in in the dia of the ring gear (or the spacing of the teeth?), with a corresponding adjustment on the pinion gear?...thus the matched sets.
Another way of asking...I'm assuming that all 9 tooth pinion gears are not the same, as they have to have an adjusted dia (or tooth spacing) to match the different ring gears....so a 9 tooth pinion gear for a 3:56 is different than a 9 tooth pinion gear for a 4:11
LOL..a third way of asking...what is the variable that allows the different number of teeth on a ring gear?
Quote from: RICH MUISE on 2015-06-11 07:14
The mystery is unraveling very quickly guys, thanks. Some more "do I have this right?"'s.....
I'm assuming that the "closer to a 1:1 ratio" that Gary mentioned, and Bob and Lynn were refering to: That is the ratio of the differential's gear to the tranny's 1st gear?
Also...the ring gear as stated can have a different number of teeth, while the pinion gear remains constant at, in our case, 9 teeth. I'm trying to figure out how a ring gear can have a differing quantity of teeth, so I'm concluding that the difference has to come in in the dia of the ring gear (or the spacing of the teeth?), with a corresponding adjustment on the pinion gear?...thus the matched sets.
Another way of asking...I'm assuming that all 9 tooth pinion gears are not the same, as they have to have an adjusted dia (or tooth spacing) to match the different ring gears....so a 9 tooth pinion gear for a 3:56 is different than a 9 tooth pinion gear for a 4:11
LOL..a third way of asking...what is the variable that allows the different number of teeth on a ring gear?
The 1:1 ratio was a hypothetical rear end ratio. The closer you get to this number the slower the engine turns.
Earlier, I was talking about the 1st gear ratios. OVERALL GEAR RATIOS should be considered in selecting a rear end ratio. The over gear ratios are determined by multiplying the rear end ratio times the transmission gear ratio in any given gear. Overall 1st gear ratios between 10 to 1 and 11 to 1 should be about right for a 4000 lb car. If your transmission 1st gear ratio is 2.84 and you have a 3.55 rear end that gives you (2.84 x 3.55) 10.08 overall in first, pretty good. My car has a wide ratio toploader (2.72) and a 3.89 rearend for an overall of 10.6 for comparison. A close ratio muncie (2.20) and a 4.56 rearend is only 10.03 overall in first gear! The difference in the overall gear ratio in high gear between these examples is very large because your transmission has overdrive. 3.55 x .7= 2.48 for your car, 3.89 for mine, and 4.56 for the hypothetical GM. The GM car is turning 4127 rpm at 70, mine 3520 rpm at 70, yours 2250 rpm at 70 (assuming 26" diameter tires).
The shape of the teeth between the ring and the pinion must match in such a way to give a specific contact pattern. They are sold in sets to get close, but a differential has to be "set up".... both gears must be shimmed to get the contact correct. When the number of teeth are changed on the ring gear, the shape of each tooth changes. I am not positive but I think the pinion gear shape (profile) can stay the same. Gear teeth actually "roll" together as they make contact, making the face of the teeth have a very specific shape. Besides that, modern rear differentials (including 57s) have hypoid gears, the teeth themselves are in a spiral pattern. This allows for a larger contact pattern, or a stronger gearset. "Lower" (higher numerically) gearsets for a fixed pinion size can transfer more torque without breaking than a "tall" gearset can.
Readers beware, the information above was recovered from a senior memory .... :003:
Great explaination, Lynn. Thanks. 3.55's it'll be then for me...as I said before, I'm not building a racer. Also, as Bill said the donor MarkViii had a 3.55, and though no speed demon off the line, they were pretty responsive, and my car is hundreds of pounds lighter than a Mark.
Now, just to clarify one more thing....we have been using both periods (3.55), which I think is correct, and colons (3:55), which I'm thinking is incorrect, and also the root cause of my past confusion because the colon implies there is a comparison between the "3" and the "55"...correct??
3:55 is a typo. 3.55 is an excellent choice!
OK..cool. I was afraid you were going to disagree and send my understanding back to square one!! To go one step further with that question...technically then, when we speak of a 3.55 ratio, the colon would come in with the full description...3.55:1 ?
3.55:1 is the correct technical term, sir. Originally, I thought your first gear was 2.4:1. I read the info wrong and looked at the ratios for an AOD. That would have made your overall gear ratio in first 8.52:1, to me that would have not been "low" enough... GIGO! (Garbage in, garbage out). I actually like the gear spacing you have it seems ideal in first and forth, much better than mine. My car has a top speed of about 100 mph, at 75 it is really humming. I plan on addressing that at some point... no substitute for overdrive!
Did a little research...my base'95 MKVIII came equipped with a 3.08 differential. (the LSC models had a 3.27 for a quicker off-the-line, mine was not an LSC). So I'm gathering from all the info, if I choose the 3.55 for my 9", it should be substantially quicker off the line than a Mark VIII, not even considering the substantial weight advantage. I guess all of this is confirming my original thoughts with my engine/drivetrain choice....reasonably quick, dependable, and economical.
I do apologize for the 3.55 error, got my book out and saw that the 3.27 was in fact the correct ratio, also for the colons, just lazy on my part.....
A little yard searching and an Explorer rear with 3.55s and a T-Lock could be found and narrowed for cheap. Many of the Explorers had T-Locks if AWD.
Guys:
I, too apologize for the many colon errors I made. Rich, I think you will be very happy with a gear around 3.5 as in the original Ford 9" rear ends or a 3.55 as in the modern 8.8 Ford rear ends. The fact that drag racing does not play a role in your thoughts should also not bother you in the type (8.8 or 9") of rear end you select. Also, either type of rear end has massive after market support.
Bob
57 AGIN
OK...now I know you guys are out to confuse me, LOL. Bob as I undewrstand it, the '57's because of the 9 tooth pinions also had the 3.55 as an option (32/9=3.5555), not just the newer variety.
like i said ford used a 3.56 ratio in the 9 inch diff till 1968.in 1969 ford went to a 3.50 ratio for the 9 inch diff.
3.55 or 3.56, depends on whose rounding off. No reason why you can't have a 10 pinion gear in a 9" rear end.